Desalination and Carbon Footprint: A Meta-Analysis of Plant‑Scale Operational Emissions for MSF and RO Technologies

Abstract

As global freshwater scarcity intensifies, driven by rapid population growth, climate change, and industrialization, desalination has increasingly become a critical water supply strategy, particularly in arid and water-stressed regions. Despite its growing adoption, desalination remains highly energy-intensive, especially due to its operational processes that contribute significantly to carbon emissions, raising significant concerns about its environmental sustainability. Available life-cycle carbon intensity estimates vary widely across studies due to differences in plant design, energy sources, system boundaries, inconsistent definitions, and outdated data, which limit comparability. We present a plant- and pilot-scale meta-analysis to quantify operational carbon dioxide emission intensities (CO₂-eq/m³) for reverse osmosis (RO) and multi-stage flash (MSF) desalination technologies. For multi-effect distillation (MED), membrane distillation (MD), electrodialysis (ED), and nanofiltration (NF), available data are primarily modeled or experimental; as such, they were synthesized qualitatively and shown for context but not pooled. Results show that reverse osmosis (RO) has an operational carbon intensity of 2.52 kg CO₂-eq/m³ (95% CI: 1.28–3.76), while multi-stage flash (MSF) averages 8.98 kg CO₂-eq/m³ (95% CI: 4.66–13.30). The higher MSF values reflect reliance on thermal energy, whereas RO emissions align with electricity intensity and specific energy consumption. Sensitivity analyses confirm the robustness of these estimates. For MED, MD, ED, and NF, reported values were highly sensitive to energy source assumptions and system boundaries. These results establish transparent, plant-scale carbon benchmarks for desalination technologies under real-world energy pathways. The findings provide a decision-relevant framework for utilities and policymakers to evaluate technology selection, guide low-carbon infrastructure investment, and align desalination expansion with climate mitigation targets.